Ferroelectric RAM (also referred to as FeRAM, F-RAM or FRAM) is a random-access memory similar in construction to DRAM but uses a ferroelectric material layer instead of a dielectric layer to achieve non-volatility. The FRAM is one of a growing number of alternative non-volatile random-access memory technologies that offer the same functionality as flash memory. However, FRAM offers advantages over flash that include that include lower power usage, faster write performance, and a much greater maximum number of write-erase cycles, for example.
Ferroelectric material in the FRAM has a nonlinear relationship between the applied electric field and the apparent stored charge. Specifically, the ferroelectric characteristic of the material has the form of a hysteresis loop, which is very similar in shape to the hysteresis loop of ferromagnetic materials. The dielectric constant of a ferroelectric material is typically much higher than that of a linear dielectric because of the effects of semi-permanent electric dipoles formed in the crystal structure of the ferroelectric material. When an external electric field is applied across a dielectric, the dipoles in the material tend to align themselves with the field direction, produced by small shifts in the positions of atoms and shifts in the distributions of electronic charge in the crystal structure. After the charge is removed, the dipoles retain their polarization state, where binary “0”s and “1”s are stored as one of two possible electric polarizations in each data storage cell. Over extreme environmental conditions and/or over time however, stored data in FRAM material can be lost.
In high-reliability (automotive, medical, space, and so forth) non-volatile (NV) memory applications, stable memory technologies are needed where data is preserved regardless of the underlying time (e.g., time between accesses or time in one particular data state) or conditions involved. In many systems, the memory is used to store a set of critical system values that once written are never changed. In many of these systems, a read only memory (ROM) may be a better solution except that the data that would be stored in ROM is often not determined or known until the product is made and the final application software revised or optimized. In such cases, a reliable non-volatile memory is needed.